This invention relates generally to an improved digital radiographic imaging and recording system which is especially useful in medical radiographic applications and more particularly to a system of said type wherein a moving fan beam of X radiation is employed in combination with photodetection means to digitize and record the optical image formed immediately responsive to X radiation.
As previously indicated, scintillator materials emit visible or near visible radiation when stimulated by x-rays or other high energy electromagnetic photons hence are widely employed in various industrial or medical radiographic equipment. In medical applications it is desirable that the scintillator output be as large as possible to minimize exposure of the medical patient to the x-ray dosage. A known class of scintillator materials considered for use in computerized tomography applications is monocrystalline inorganic compounds such as cesium iodide (CsI), bismuth germanate (Bi.sub.4 Ge.sub.3 O.sub.2), cadium tungstate (CdWO.sub.4), calcium tungstate (CaWO.sub.4) and sodium iodide (NaI). Another known class of scintillator materials comprises polycrystalline inorganic phosphors including europium activated barium fluorochloride (BaFCl:Eu), terbium activated lanthanum oxybromide (LaOBr:Tb), and thulium activated lanthanum oxybromide (LaOBr:Tm). A still third class of already known scintillator materials found useful in computerized tomography comprises various dense sintered polycrystalline ceramics such as rare earth doped yttria/gadolinia (Y.sub.2 O.sub.3 /Gd.sub.2 O.sub.3) and polycrystalline forms of said previously mentioned phosphors including BaFCl:Eu, LaOBr:Tb,CsI:Tl, CaWO.sub.4, and CdWO.sub.4.
In U.S. Pat. No. 4,383,327, there is disclosed a scanning slit electronic radiographic system employing a linear array of electronic radiation detectors to digitize and record the optical image formed in an image intensifier device when stimulated by X radiation after passage through a medical patient. It is recognized in said prior art disclosure that an image intensifier device is subject to various problems of scattered radiation producing distortion and loss of information details in the optical image being formed. It is still further recognized in said prior art disclosure that such radiation scattering in the image intensifier device requires an increased exposure of the patient to radiation in order to prevent such degradation of the image quality and which is an undesirable consequence for medical radiographic applications. The emerging optical image from said image intensifier device in said prior art radiographic system is optically focused upon remotely located charge coupled devices forming the photodetection means in said system thereby occasioning additional detection efficiency losses in the optical information being retrieved such as resolution and contrast losses. The physical orientation of charge coupled devices forming the photodetection means in said prior are radiographic system consists of parallel aligned columns and rows in a spaced apart configuration. Such a spaced apart configuration creates void spaces whereby still further optical information can be lost for an inaccurate representation of the optical information being retrieved.
A staggered physical orientation for said photodetection means is disclosed for a digital radiographic system of the same type in a publication entitled "X-ray Image Sensor Based on an Optical TDI-CCD Imager" authored by J. deGroot, J. Holleman, and H. Wallinga and issued by Oldelft Optical Industries. Said improved photodetection means is reported to be physically coupled to the exit window of an image intensifier device to provide a more unbroken and thereby more accurate representation of the optical information being retrieved. By further reason of the relatively complex and fragile nature of the image intensifier device being employed in both prior art radiographic imaging systems, however, said devices are seen to remain stationery while being operated with the patient being moved during exposure to the x-ray fan beam such as positioned on a movable table aligned therewith. Understandably, any involuntary movement of the medical patient in either prior art radiographic imaging process creates still another source of error, such as blurring, in the optical image being formed.
It remains desirable, therefore, to provide an improved digital radiographic imaging system of this general type which is not subject to the inherent limitations experienced when using an image intensifier device.
It is another important object of the invention to provide a more compact and rugged as well as simplified equipment system and method for digitally recording a radiographic image as formed and in a manner providing improved quantum detection efficiency.
Still another important object of the present invention is to provide such an improved digital radiographic imaging system that is relatively inexpensive as well as more reliable to construct and operate while further not experiencing loss in the principal benefits now achieved with a radiographic technique of this type.